Zoology and wildlife conservation

Spectroscopic evidence for a pseudogap in the normal state of underdoped high-T(sub c) superconductors

Article Abstract:

A pseudogap is present below a temperature (T*) that is greater than the superconducting transition temperature (T(sub c)) in the normal state of underdoped samples of Bi2Sr2CaCu2O(8+delta). The presence of the pseudogap is indicated by experiments measuring the momentum-resolved electron excitation spectrum of CuO2 planes using angle-resolved photoemission spectroscopy. The pseudogap has a d-wave symmetry and forms the d-wave superconducting gap when phase coherence is generated below T(sub c). The value of T* decreases with an increase in doping.

Destruction of the Fermi surface in underdoped high-Tc superconductors

Article Abstract:

The temperature dependence of the Fermi surface in underdoped Bi(sub2)Sr(sub2)CaCu(s8b2)O(sub8+delta) was examined using angle-resolved photoemission spectroscopy. On cooling the pseudo-gap was found to open up at different temperatures for different points in momentum space, resulting in the initial breakup of the Fermi surface. This occurs in the absence of long-range order.

The origin of multiple superconducting gaps in MgB2

Article Abstract:

The direct experimental evidence for the two-band superconductivity in MgB2, by separately observing the super conducting gaps of the alpha and phi bands, is reported. The gaps have distinctly different sizes, which unambiguously establishes MgB2 as a two-gap superconductor.